According to our sources, Shayna runs in one of those hot blonde Hollywood crowds filled with Instagram models who pretty much party exclusively at rich people's houses. And that's how Seacrest met her roughly a year ago.

It's unclear if Ryan and Shayna are boyfriend and girlfriend ... or just "close" friends.

Fun fact: Shayna's the same girl who was pictured smooching with Terrence Howard last year in St. Barts.

It's unclear exactly how long they've been seeing each other ... but Seacrest has been a free man since March, when he ended things with Julianne.